PHILADELPHIA (CBS) — Monday is the first day of school for many children in the Delaware Valley. The day will start mildly with temperatures between 18 and 20 degrees at 7 a.m.

You’ll need to dress for a warm day with temperatures in the 30s and a mix of cloud and sun. There’s a chance of a few isolated showers, especially in the afternoon. It will remain dry across much of the region.

Summery warmth will return on Tuesday and Wednesday, with highs of 35 to 35 degrees Celsius, higher humidity and a heat index of 35 to 35 degrees Celsius. Tuesday will be dry and sunny, but Wednesday will become increasingly cloudy with the possibility of isolated showers and perhaps a few thunderstorms.

Temperatures will fall to around 30 degrees again on Thursday, with partly cloudy skies. There is an increasing chance of rain showers and thunderstorms on both days of next weekend.

This was a rare dry weekend for Philadelphia, only the third dry weekend of 13 weekends since Memorial Day. That means only 23% of our weekends were dry and 77% had rain. Looking ahead to Labor Day weekend, there is a chance of scattered showers and thunderstorms on both Saturday and Sunday.

Here is your 7-day forecast:

Monday: High: 87, Low: 66, Showers or thunderstorms possible

Tuesday: High 89, low 66, mostly sunny

Wednesday: High 96, low 72, hot, later a storm

Thursday: High 82, low 73, partly cloudy

Friday: High 80, low 67, partly cloudy

Saturday: High 81, low 68, isolated storms

Sunday: High 85, low 70, isolated storms